This invention relates to a method of removing an oxide on a metal surface, and more particularly to a method of removing a metal surface oxide as is suitable for preventing the corrosive damage of a metal being a parent material.
On those inner surfaces of equipment and piping installed in a thermal power plant, nuclear power plant, chemical plant or the like plant which come into contact with a fluid, an oxide adheres or grows with increase in the operation years of the plant. Since such oxide is feared to hamper the functions of the equipment and the piping, it is desired to be removed.
Especially in the nuclear power plant, radioactive ions in cooling water which flows within the nuclear power plant stick to the oxide adherent on the inner surfaces of the equipment and piping of the plant or are accepted into the oxide during the growth of the films of the oxide which are formed on the inner surfaces of the equipment and piping. In consequence, the radiation doses of the surfaces of the equipment and piping increase. This hinders the maintenance and inspection of the equipment, the piping etc., and conspicuously prolongs the period of time required for the maintenance and inspection. Also to the end of readily executing the maintenance and inspection in a short time, the oxide formed on the inner surfaces of the equipment and piping need to be removed on occasion.
Methods of removing an oxide from a metal surface as have heretofore been often performed use a solution in which an acid, a complexing agent and a reducing agent are mixed, as disclosed in the official gazettes of Japanese Patent Publication Nos. 731 (1978) and 20252 (1978). With such methods, the metal of the parent material is also corroded and damaged.